The invention relates generally to mail processing machines and in detail to a rotary feeder, in particular for inserting enclosures into conveying compartments of an enclosure-collating path.
Such rotary feeders which have a feeder drum which can be made to rotate by a drive motor, via a gear mechanism forming a drive unit with the drive motor and fastened on a drive shaft coupled to the gear mechanism have been on the market for some time. On the feeder drum, pairs of claws are mounted on pivoting shafts, can be pivoted in radial planes in relation to the feeder-drum axis of rotation and can be moved into an open position counter to the prestressing force of prestressing means or spring means, via cam follower rollers and a housing-mounted cam, as the drum rotates, counter to the force of the spring means and into a closed position by the spring force of the prestressing means or spring means as the drum rotates further, such that the claws of a pair of claws grip an enclosure edge of a respectively lowermost enclosure of an enclosure stack and, as the drum continues to rotate, draw this lowermost enclosure out of the enclosure stack and guide the enclosure around the drum circumference and, for example, transport it in the direction of a conveying compartment of an enclosure-collating path.
If the enclosures to be handled by the rotary feeder have a length in the circumferential direction of the feeder drum of less than half the feeder-drum circumference, during a complete feeder-drum rotation, two enclosures can be deposited in successive conveying compartments of the enclosure-collating path as a result of the fact that the feeder drum is provided at two diametrically opposite points with cam-actuated pairs of claws in each case, of which one pair of claws grips the enclosure edge of the lowermost enclosure of the enclosure stack while the other pair of claws releases the leading enclosure edge of an enclosure gripped previously and conveyed around the feeder-drum circumference by means of moving the claws of the relevant pair of claws in the opening direction, so that this enclosure is then deposited, for example in the conveying compartment of the enclosure-collating path.
In order to ensure secure gripping of the leading enclosure edge by clamping the same between the tips or front ends of the claws of the pair of claws, on the one hand, and supporting parts fastened to side surfaces of the feeder drum on the other hand, the claws are spring-loaded via very powerful prestressing springs about their pivot axes mounted on the feeder drum, which has the effect that, when the follower roller, which is coupled to the pivoting shaft of a pair of claws via a link and which is assigned to a pair of claws opening counter to the prestressing force of the prestressing means, rides up from small radii to a large radius at a transition of the cam, mounted so as to be stationary, a considerable braking moment acts on the feeder drum. On the other hand, moving the follower roller assigned to a closing pair of claws down at a transition from large radii to small radii of the cam, mounted so as to be stationary, when this follower roller is pressed on via the link by means of the powerful prestressing means of this pair of claws, has the effect that, in the closing phase of a pair of claws, a powerful accelerating moment is exerted on the feeder drum.
A chronologically quick succession of an accelerating moment and a decelerating moment during the drum rotation has the effect of shocks in the gear mechanism of the drive unit of the feeder drum within the gear mechanism play, which intensify the wear of the gear mechanism, stress the mounting of the drive unit and cause an unpleasant noise.
Furthermore, the short-term succession of the aforementioned accelerating moment and of the braking moment can lead to oscillation of the drive speed of the feeder drum, in such a way that, for example after gripping the leading enclosure edge of the lowermost enclosure of the enclosure stack and drawing this enclosure out of the enclosure stack, the circumferential speed of the feeder drum decreases suddenly or even a short-term reversal of the direction of rotation occurs, which results in the enclosure currently to be drawn out of the enclosure stack curving up somewhat and, after the regular rotation of the feeder drum has been resumed, being tensioned and then placed on the circumference of the feeder drum again with a cracking noise.